The present invention is concerned with novel water-soluble racemic or optically active tetrasulfonated diphosphine compounds of the formulae ##STR2## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 independently signify lower alkyl or lower alkoxy;
m and n are 0, 1 or 2; and PA1 X signifies hydrogen, an alkali metal, an earth alkali metal or an ammonium ion; PA1 m and n are 0, 1 or 2; and PA1 X signifies hydrogen, an alkali metal, an earth alkali metal or an ammonium ion; PA1 wherein Z represents halogen or the group A--COO, wherein A represents lower alkyl, aryl, halogenated lower alkyl or halogenated aryl, wherein L represents a racemic or optically active diphosphine ligand of formulae I or II. PA1 wherein L represents a racemic or optically active diphosphine ligand of formulae I or II,
with the provision that R.sup.3 is located in position 4 or 5, and R.sup.4 is located in position 4' or 5'.
The invention is also concerned with the manufacture of compounds of formulae I and II, particularly in their optically active form, i.e. in the (R)- and the (S)-form. Furthermore the invention is concerned with complexes of compounds of formulae I and II, particularly in their optically active forms ((R)- and (S)-form) with transition metals of Group VIII, especially with ruthenium, rhodium, palladium or iridium. These complexes are useful as homogeneous catalysts in asymmetric reactions such as e.g. asymmetric hydrogenation, enantioselective isomerisation, and the like.
It is known that separation of the catalyst from the reaction products and recovery of the catalyst are, next to the activity and selectivity of the catalyst, of major importance to industrial applications of homogeneous catalytic processes. Although catalyst separation is sometimes readily achieved, e.g. in the case of volatile products which can be distilled from the catalyst, it may be more difficult in the case of crystalline products, where co-crystallisation or inclusion may cause problems resulting in intolerable amounts of metal traces in the reaction product. Catalyst recovery and catalyst recycling are generally difficult to achieve in an economically and ecologically-sound way, but are of paramount importance in catalytic reactions which require relatively large amounts of catalyst.
To resolve the problem of catalyst recovery and catalyst recycling, two major approaches--each of its own attractiveness--exist. One of them is the heterogenization of a homogeneous catalyst by anchoring the catalyst or catalyst precursor to an inert support. However, decreasing activity of the heterogenized catalyst due to metal leaching into solution is often observed. A second approach has lead to the development of complexes of water-soluble ligands with transition-metals as catalysts. Such complexes can be used in various ways, e.g. in aqueous solvent systems, in biphasic systems consisting of water and a non-miscible organic phase or in organic systems alone with a subsequent removal of the catalyst by aqueous extraction. Biphasic systems with or without cosolvents, with recycling of the aqueous phase containing the catalyst, recently have been introduced into technical practice. For example, a water-soluble rhodium-phosphine complex, e.g., the sodium salt tris(m-sulfonatophenyl)phosphine), has been used as a catalyst in the preparation of aldehydes by hydroformylation of olefins. The use of such catalysts comprised of water-soluble ligands complexed to transition metals does not only resolve the catalyst-product separation but does contribute to the economy and ecology of the processes by using water as a benign solvent. However, these water-soluble transition metal-phosphine catalysts in the prior art have limited use as catalysts for asymetric reactions, since the sulfonato groups located in the meta position cause steric effects on the asymmetric induction in these reactions.